Insensitive Munitions – US Problems and Solutions
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Insensitive Munitions – US Problems and Solutions Kenneth J. Graham, President and Chief Technical Officer Judson Consulting Service, Warrenton, VA USA [email protected] ABSTRACT This paper describes some of the problems in implementing insensitive munitions requirements in the United States, and solutions that have been applied. Mr. Graham has worked in this area for over 43 years, and the views expressed are his own. All information is unclassified and releasable to the public. 1.0 INTRODUCTION The phrase “Insensitive Munitions” seems to be incongruous. “Munitions” implies weapons that are sensitive to their boosters or igniters; while “Insensitive” implies that the weapons aren’t. So to start out, some definitions are in order. • Munition – An assembled ordnance item that contains explosive material(s) and is configured to accomplish its intended mission. • Insensitive munition – Munitions which reliably fulfil (specified) performance, readiness and operational requirements on demand, but which minimize the probability of inadvertent initiation and violence of subsequent collateral damage to the weapon platform (including personnel) when subjected to unplanned stimuli. • Burning – The least violent type of explosive event. The energetic material ignites and burns, non- propulsively. The case may open, melt or weaken sufficiently to rupture nonviolently, allowing mild release of combustion gases. Debris stays mainly within the area of the fire. The debris is not expected to cause fatal wounds to personnel or to be a hazardous fragment beyond 50 ft. • Hazardous fragment – For personnel, a hazardous fragment is a piece of the reacting weapon, weapons system or container having an impact energy of 58 ft-lb [79 J] or greater. • Deflagration – Reaction driven by thermal conduction in an energetic material. For solids and liquids, no utilization of atmospheric oxygen is required. The reaction wave is subsonic in the energetic formulation and the reaction products flow in a direction opposite to the reaction front. • Detonation – Chemical reaction induced by a compression wave and driven by the expansion wave in the products. A shock wave is formed that propagates at a steady velocity if the formulation is above its critical diameter. The velocity of the shock wave in the explosive (detonation velocity) is supersonic, and the reaction products travel in the direction of the shock wave. • Critical diameter – The diameter of a long, unconfined right circular cylinder of energetic formulation that just sustains a steady detonation. Propagation of detonation fails below critical diameter. STO-EN-AVT-214 5 - 1 Insensitive Munitions – US Problems and Solutions Figure 1. Cylindrical Critical Diameter Test. • Sympathetic reaction – The detonation of a munition or an explosive charge induced by the detonation of another like munition or explosive charge. • Explosive - Substances or mixtures of substances which are capable of undergoing exothermic chemical reaction at extremely fast rates to produce gaseous and/or condensed reaction products at high pressure and temperature. • Detonation reactions take place in microseconds • Energy release rates are ~ 4000 J/g • Power level of energy conversion is ~5 x 109 W/cm2 at detonation front. (For comparison, the total US electrical generating capacity (in 1960) was 3 x 1011 W.) Some reference explosive molecules include TNT, RDX and HMX. Figure 1 gives some typical values for the detonation of TNT, while Figure 2 shows some properties for the much higher performance explosive HMX. CH3 O2N NO2 NO2 2,4,6-trinitrotoluene (TNT) Figure 2. Detonation properties of TNT. 5 - 2 STO-EN-AVT-214 Insensitive Munitions – US Problems and Solutions NO2 H2C N CH2 O2N N N NO2 H2C N CH2 NO2 1,3,5,7-tetranitro-1,3,5,7-tetraaza- Cyclooctane, (HMX) Figure 3. Detonation properties of HMX. There are numerous potential hazards associated with munitions. They are sensitive to thermal and shock or impact stimuli, with potential responses ranging from none to very severe combinations of reactions. Figure 4 illustrates. Figure 4. Potential Hazards from Munitions 2.0 US PROBLEMS. HISTORICAL DRIVERS TO REDUCE MUNITIONS SENSITIVITIES – OR – OUR OWN WEAPONS ARE KILLING US! In order to fulfil their missions, the US services need to have functional personnel and materiel. A way to accomplish this is to have munitions that do not react violently to inadvertent threats, destroying personnel and materiel. In particular, fire is a significant threat. A few examples of what drove the US to implement insensitive munitions research and development follow. STO-EN-AVT-214 5 - 3 Insensitive Munitions – US Problems and Solutions 2.1 US Navy The US Navy experienced several inadvertent violent reactions of munitions aboard ship, causing loss of life and major materiel damage. Estimates for three shipboard accidents approached 2 billion dollars and loss of functionality. An example is the USS Forrestal incident. A ZUNI rocket was fired accidentally from an aircraft being readied for a mission on July 29, 1967. The rocket screamed across the flight deck, struck another aircraft and ignited a fuel fire (Figure 5(a). The initial fire could have been contained, but 90 seconds after the fire started a bomb detonated, killing or seriously wounding most of the fire fighters. The detonation ruptured the flight deck, and burning fuel spilled into the lower levels of the ship (Figure 5(b). Bombs, warheads, and rocket motors exploded with varying degrees of intensity in the fire, killing 134 and wounding 161 men. Twenty-one aircraft were destroyed. (a) (b) Figures 5. (a) Raging fuel fire on Forrestal deck; (b) Hole in carrier deck after bomb detonated in fast cookoff. 2.2 US Army The US Army experienced the inadvertent violent reaction of munitions due to fire, causing loss of life and major materiel damage at Camp Do-Ha (Black Horse Camp) in Kuwait. 56 persons were killed and damage estimates were over 50 million dollars, again resulting in loss of functionality. The first incident occurred on 11 July 1991. Defective heater in ammunition carrier started a massive fire (Figures 6(a) and 6(b)). 53 soldiers died in fast cookoff of 155mm Howitzer shells and other munitions. The second incident occurred on 24 July 1991, where 3 more soldiers were killed clearing the site. It is of note that more tanks were destroyed in the accident than in the war (14 M1-A1’s). 5 - 4 STO-EN-AVT-214 Insensitive Munitions – US Problems and Solutions (a) (b) Figures 6. (a) Location of ammo carrier with defective heater; (b) Overview of damage following fire. 2.3 US Air Force Though not an adverse munition reaction to a threat, in a related situation, the sensitivity of Tritonal-loaded bombs became an issue for storage in Germany. The Air Force needed to store a large number of hazard class 1.1 (mass detonating) bombs in an area that was surrounded by civilian population, but the number of bombs that could be stored was severely limited by the required quantity-distance requirements. They chose to develop a new insensitive bomb fill for MK-82 bombs that gave the munitions a hazard classification of 1.6 (Extremely Insensitive Articles). The change in quantity distance requirements was dramatically affected, allowing many more bombs to be stored in the same area. Figure 7 illustrates. HC 1.6 HC 1.6 Saves: Figure 7. Dramatic reduction in inhabited building Q-D by changing from HC 1.1 Tritonal to insensitive HC 1.6 PBX explosive. STO-EN-AVT-214 5 - 5 Insensitive Munitions – US Problems and Solutions 2.4 SOLUTIONS With the disastrous incidents with our own munitions reacting violently to unplanned stimuli, it was clear something had to be done. The US Navy led the way. In 1984, the Navy’s IM program was established. Collaboration with experts in the field of energetics was key. The Navy established the Insensitive Munitions Advanced Development program that included key government and industry technical personnel helping to understand threat stimuli and modes of reaction; and the sensitivities of energetic ingredients and formulations. Life-cycle based threat hazard assessment of weapons was implemented. Working groups assessed the potential sensitivities of munitions and prepared priority lists. Military Standards were promulgated and generic IM tests were developed and continually refined addressing shock and impact as well as thermal threats. Weapons were subjected to the IM tests and impartially scored to assess the current state of the art and to identify problems and areas for potential fixes. These were tabulated in 1985 in the first Technology Status Chart (figure 8). You will note the large amount of red indicating detonation and yellow indicating deflagration as the mode of reaction. Figure 8. IM Technology Status chart 1985 [1] 5 - 6 STO-EN-AVT-214 Insensitive Munitions – US Problems and Solutions This work expanded to the other services (1987 Joint MOA on IM). The problem was where to store the baseline IM test data, energetics information, and test results with mitigation applied. The Navy developed a first generation IM database where the records and reports were physically stored and then incorporated in searchable electronic database. The US allies were also implementing IM testing and improvements to their weapons systems. It soon became apparent that an international information center was needed and in 1991 the NATO IM Information Center (NIMIC) opened in Brussels, Belgium. The database function was transferred to NIMIC, and IM information made available to member NATO allies. NIMIC hosted numerous international workshops on various aspects of IM, and published the results in their databases. In 1995 NATO released policy and technical requirements for insensitive munitions. In 1996, IM requirements were promulgated as part of the US acquisition policy in DoD 5000.2-R. and later as US public law (Figure 9). “The Secretary of Defense shall ensure, to the extent practicable, that munitions under development or procurement are safe throughout development and fielding when subjected to unplanned stimuli.” Figure 9.